The wear on slurry transportation pipelines within the oil sand industry is a major driver of both downtime and capital expenditure. Oil sand slurries are reasonably concentrated (>35% solids by volume), typically having a sand particle diameter between 0.18 and 0.3 mm and rocks and lumps to about 125 mm, which are transported at reasonably high velocities (3 to 5.5 m/s), In an oil sand mining operation, there are a number of pipelines which contain settling slurries. An example of two major slurry pipeline systems, among others which exist in an oil sand mining and extraction operation, are oil sand hydrotransport pipelines, which carry concentrated slurries of oil sand and water from the mine to the extraction plant, and coarse tailings pipelines, which carry a concentrated slurry of sand, clay fines and water from the extraction plant to the sand storage/disposal area. Other examples include coke slurry pipelines to transport coke produced during upgrading and composite tails pipelines.
As with most conventional slurry pipelines, oil sand slurry pipelines are operated above a threshold operating velocity to ensure that a blockage does not form due to the deposition of solids present in the slurry. This threshold velocity is known as the deposition velocity, the velocity at which the deposition of solids occurs. Generally, the minimum operating velocity is usually kept as 0.5 m/s more than the deposition velocity (Kaushai et al., (2002) Powder Technology, vol. 125, Issue 1, 89-101). The deposition velocity is commonly measured in laboratory settings by locating a gamma ray densitometer at 5% of the pipe diameter from the lower pipe surface and the density at this location is monitored while the pipeline velocity is decreased. When the density reaches a value that corresponds to the solid packing density for the particular material, the deposition velocity has been reached. If the velocity is reduced further below the deposition velocity, the pipeline will become progressively more filled with a bed of particles and at some point the pumping capacity of the system will not be able to overcome the increased pressure gradient within the pipeline. At this point, it is necessary to shut the system down to clear out the blockage and the pipeline can be said to have “sanded-off”. Thus, for a given volumetric throughput of material, the pipe diameter must be chosen to ensure that solids deposition does not occur. In the design of industrial scale pipelines, computerized models are used to predict the deposition velocity apriori. The deposition velocity as measured in a laboratory setting is included in these computerized models and the models can then be used to predict the deposition velocity within commercial pipelines.
Pipeline wear is proportional to the pipeline velocity and having to operate above the deposition velocity can lead to accelerated wear rates. Operating above the deposition velocity leads to either a sliding bed being present on the pipe bottom or a relatively quick moving region of higher density material. Since erosion is dependent upon both the flow velocity and the particle concentration, both of these scenarios lead to high wear rates on the pipe bottom. Thus, typically, the pipelines have to be maintained by frequent rotations, increasing the wall thickness, or by costly upgrades, e.g., using pipes having a non-metallic lining such as rubber, urethane, etc.